When retrofitting a system to R134a, which oil is used?

• A. Polyether
• B. Polyester
• C. Mineral oil
• D. PAG oil

Answer: (B)

Retrofitting to R134a requires a lubricant that mixes well with the new refrigerant and works with the system materials. Mineral oil—the oil used with older refrigerants like R-12—does not mix with R134a and can separate, leaving the compressor inadequately lubricated. Polyester oil, or POE, is designed to be miscible with R134a and is compatible with the seals and gaskets commonly found in systems upgraded to this refrigerant. That’s why polyester oil is the standard choice for these retrofits. While some automotive A/C kits use PAG oil and others might use different synthetic oils, the conventional retrofit guidance centers on polyester oil as the appropriate lubricant for R134a.